I mostly use Perle 8 but have also used a size 12 thread, which is a slightly thinner strand than the Perle 8. Both work well.
Big stitch is my favorite quilting method. Although I started quilting 30 years ago, I've never been able to master the rocking method, but big stitch is the perfect technique for the stab stitcher that I am. Years ago a quilt shop saleslady told me my quilt would look terrible with big stitches in a contrasting thread color. Apparently she wasn't familiar with the style and couldn't conceive of it being a valid method of quilting. I've always loved the ease of it and the character it adds. It's been really nice to see it gain in popularity in recent years. Jen Kingwell and Sarah Fielke are well respected quilters and have done a lot to bring the big stitch method into the public eye.